Hydraulic circuits and control systems are incorporated into a host of machines and equipment, such as but not limited to, hauling machines, dump trucks, mining vehicles, on-highway vehicles, trains, motor graders, loaders, excavators, earth-moving vehicles, dozers, tractors, backhoes, agricultural equipment, material handling equipment, power generators, and the like. Moreover, the hydraulic circuits and control systems may be configured to distribute and control a supply of pressurized fluid which is circulated throughout the machine and utilized for performing one or more tasks. For example, the machine components such as, motors, actuators, tools, and other known devices may use the pressurized hydraulic fluid for the actuation, rotation, operation, or other action of machine components.
Furthermore, hydraulic circuits and control systems may rely on one or more pumps to circulate and distribute the pressurized fluid to the hydraulic components. In some cases, the machine may include multiple hydraulic components which require different pressure and flow rates of hydraulic fluid for performing the necessary actuation, rotation or other hydraulic functions. As a result, some hydraulic circuits and control systems configure the pumps to operate at one setting which circulates the hydraulic fluid at a fixed pressure. The hydraulic circuit and control system will then use a set of control valves and other components to regulate the flow and pressure of the hydraulic fluid needed by each of the different hydraulic components.
Hydraulic system configurations that provide hydraulic fluid at a fixed pressure may work well for machine implements and components such as but not limited to, a hammer, a drill, or other such oscillating implements because the constant pump pressure helps maintain stability of the hydraulic fluid pump during implement operation. Moreover, variable or load responsive hydraulic system configurations may work well for machine implements and components such as but not limited to, a tramming motor, and other known load responsive components because the use of the variable or load responsive flow and pressure may save power and energy that is otherwise wasted. However, variable or load responsive hydraulic systems may be more difficult to control, and therefore not well-suited for use with oscillating machine implements and components. In some cases, the oscillating nature of the machine implements may cause instability within the variable or load responsive hydraulic system and an unstable system may lead to premature wear of the system components and increased hydraulic noise.
Accordingly, a desire and need exists for improved control of hydraulic circuits and systems.
A hydraulic system with a pump that furnishes pressurized fluid to a supply node connected to a plurality of functions is disclosed in U.S. Pat. No. 9,303,387B2 (hereinafter the “'387 application”), entitled, “Hydraulic System with Open Loop Electrohydraulic Pressure Compensation.” The hydraulic system of the '387 application includes a variable displacement pump that is configured to provide pressurized fluid to an outlet. The hydraulic system further includes a conventional load sense mechanism that is used to control the output of the variable displacement pump. Furthermore, a controller may be added to the hydraulic system for controlling the output of the pump. Moreover, the controller is configured open and close hydraulic system valves to proportionally control the flow of fluid during the hydraulic system operations. However, the electronic device of the '387 patent does not provide a control valve configuration which provides the capability of the hydraulic system to switch between a variable pump mode and a fixed pump mode. Furthermore, the electronic device of the '387 patent does not provide the ability to control the variable pump between multiple modes, with each mode capable of limiting and maintaining a different maximum pump pressure.